1. Field of the Invention
The present invention relates to a method of pH control, and more specifically to a vacuum operated boiler condensate/feed water pH adjustment system using anhydrous ammonia.
2. Description of Related Art
It is known to use ammonia to control the pH of demineralized water in a condensate and feed (condensate/feed) water system of power plants. For example, in one conventional system, aqueous ammonia is fed into the condensate/feed water system via chemical feed pumps to adjust the pH. In another conventional system, anhydrous ammonia is fed into the water flow via mass flow meters from pressurized tanks. Both of these systems will adjust the pH. Thus, while using both aqueous and anhydrous ammonia is known to control pH, neither of these systems can perform the task of controlling the pH in a safe manner, while using a contaminate-free ammonia solution.
There are at least two problems with using aqueous ammonia to adjust the pH of condensate/feed water systems. First, a reagent can become contaminated. In the production of aqueous ammonia, gas is bubbled through water to form the aqueous solution. If the water used in the process is not pure, the contaminates can become a part of the ammonia solution. These contaminates can, and often will, cause problems within power plant systems.
A second problem with using aqueous ammonia to adjust the pH is the low boiling point of aqueous ammonia. For instance, 30% aqueous ammonia will boil at 83 degrees Fahrenheit. The combination of a high ammonia concentration and moderately high environmental temperatures often causes the ammonia within the pump to vaporize, rendering the pump inoperable.
Using a pressurized anhydrous ammonia feed system does not have the same problems as those associated with using aqueous solutions, but can increase the risk of a catastrophic ammonia release due to a pipe or fitting leak. Such a release can have disastrous consequences to plant operating staff as well as nearby populations, as ammonia is a toxic gas.
An example of a conventional power plant water conditioning system includes that shown in U.S. Pat. No. 5,715,290 to Uetake et al., which discloses a reactor water control method in a boiling water reactor (BWR) power plant, wherein the BWR power plant has a low radioactivity concentration reactor water and fuel clad tube for the BWR. Uetake et al. discloses a method of controlling the pH of reactor water in the initial stage of an operation cycle after loading new fuel roads, in a range greater than 7 and less than 9, and, after a predetermined period in the same operation cycle, can reduce the pH of the reactor water below 7. Uetake et al. teaches the use of Be, Zr, Al, Nb, Y and Ti (Beryllium, Zirconium, Aluminum, Niobium, Yttrium, and Titanium) to be fed into the reactor water for pH adjustment.
U.S. Pat. No. 5,230,810 to Clark et al. discloses a corrosion control system for wet oxidation systems. Clark et al. discloses a process for controlling corrosion in a wet oxidation system by controlling the operating pH range within the system. A pH operating range is selected within which corrosion to the wet oxidation system preferably is minimized. The pH within the wet oxidation system is monitored, and a pH adjusting material is added to the waste material being treated to maintain the system pH within the selected pH range, accordingly minimizing corrosion. Clark et al. discloses the generation of wet oxidation by ammonia, amines, or carbon dioxide.
U.S. Pat. No. 4,950,449 to Peterson et al. discloses the inhibition of radioactive cobalt deposition in water-cooled nuclear reactors. Peterson et al. discloses the effective inhibition of radioactive cobalt deposition may be achieved by the continuous addition of zinc oxide to the water entering a water-bearing vessel of the reactor throughout the operation of the reactor. Accordingly, this system can provide steady control of radioactive cobalt accumulation, as well as efficient use of zinc oxide. Thus, Peterson et al. teaches the addition of zinc oxide to the water supply.
U.S. Pat. No. 4,940,564 to Aizawa et al. discloses the suppression of the deposition of radioactive substances in BWRs, particularly in a nuclear power plant. The Aizawa et al. method for suppressing deposition of radioactive substances onto the surfaces of out-of-core components in a boiling water-type, nuclear power plant is characterized by injecting an alkaline element into reactor water in the presence of an amount of the oxygen formed by nuclear fission of the reactor water and dissolved in the reactor water, particularly without hydrogen gas injection, during the nuclear heat up operation period of a boiling water-type nuclear power plant. The reactor water containing the injected alkaline element is circulated through the primary cooling water system of a nuclear reactor, thereby forming an oxide film on the surfaces of out-of-core components in the primary cooling water system of the nuclear power plant.
U.S. Pat. No. 3,612,087 to Roland discloses a water treating device. Roland teaches a device for treating water by controlled injections of bromine. A bromine storage vessel communicates with a dilution vessel-suction pump, which continuously circulates water to be treated therethrough to maintain a negative pressure in the storage vessel. A dosing means communicates with the vessel to intermittently transmit predetermined amounts of brominated water to the dilution vessel.
Therefore, it can be seen that a need yet exists for a pH adjustment system that limits or eliminates vapor locking issues, limits or eliminates contamination of condensate issues, and provides a safe means of pH adjustment to the condensate/feed water system of a power plant. It is to the provision of such a system, preferably, a vacuum actuated and sustained ammonia feed system for the pH adjustment of power plant condensate and boiler feed water, that the present invention is primarily directed.